Method for regulating the transmitting power of a master station, and corresponding master station

ABSTRACT

A method for regulating the transmission power (P) of a transmitting station ( 10 ) and a transmitting station ( 10 ) are proposed which enable the fastest possible adaptation of a measured signal/interference ratio (SIR) to a specified target value (SIR z ). The method is employed in a transmission system as a function of an estimate of the signal/interference ratio (SIR) in a receiving station ( 20 ), and on the basis of an instruction (TPC) of the receiving station ( 20 ) the transmission power (P) in the transmitting station ( 10 ) is changed. The amount of the change (DeltaP) in the transmission power (P) is adjusted as a function of a power ratio (P/Pmean) between the current transmission power (P) and an average over time (Pmean) in the transmission power (P), such that when the value of the power ratio (P/Pmean) is increasing, the amount of the change (DeltaP) in the transmission power (P) is also raised.

PRIOR ART

[0001] From German Patent Application 199 58 383.8, which had not yetbeen published by the priority date of the present application, a methodfor regulating the transmission power of a transmitting station in atransmission system as a function of an estimate of thesignal/interference ratio in a receiving station is known in which thetransmission power in the transmitting station is changed on the basisof an instruction from the receiving station.

ADVANTAGES OF THE INVENTION

[0002] The method according to the invention for regulating thetransmission power of a transmitting station, and the transmittingstation according to the invention, as defined by the characteristics ofthe respective independent claims, have the advantage over the prior artthat the amount of the change in the transmission power is adjusted as afunction of a power ratio between the current transmission power and anaverage over time in the transmission power, such that when the value ofthe power ratio is increasing, the amount of the change in thetransmission power is also raised. In this way, the transmission powercan be adapted faster and more precisely to the properties of thetransmission channels of the transmission system. The deviation in thesignal/interference ratio, measured in the receiving station, from aspecified target value can thus be kept as slight as possible. Atrelatively high speeds between the transmitting station and thereceiving station, it is thus possible above to compensate for rapid,deep attenuation incursions on a transmission channel between the twostations. Errors in transmission are thus reduced.

[0003] Another advantage is that to perform the method of the invention,changes are needed in a conventional transmitting station on to theextent that an evaluation unit is provided, which by the method of theinvention changes the transmission power of the transmitting station asa function of the instruction received from the receiving station. Nomodification of the receiving station is needed for performing themethod of the invention.

[0004] By the provisions recited in the dependent claims, advantageousrefinements and improvements can be made in the method for regulatingthe transmission power of a transmitting station and in the transmittingstation itself, as defined by the independent claims.

[0005] It is especially advantageous that the relationship between thepower ratio and the amount of the change in the transmission power isselected to be nonlinear. In this way, rapid, deep attenuationincursions in the transmission of signals from the transmitting stationto the receiving station can be compensated for even faster, because thetransmission power of the transmitting station can be readjusted evenfaster. The deviation of the estimated signal/interference ratio fromthe specified target value can thus be kept even smaller.

DRAWING

[0006] One exemplary embodiment of the invention is shown in the drawingand explained in further detail in the ensuing description.

[0007]FIG. 1 is a block circuit diagram of power control between atransmitting station and a receiving station;

[0008]FIG. 2 is a flowchart for the mode of operation of the method ofthe invention;

[0009]FIG. 3 shows a course over time of the reception field intensityof the receiving station and the optimal transmission power of thetransmitting station; and

[0010]FIG. 4 shows a nonlinear characteristic curve for the change inthe amount of the transmission power, referred to a power ratio.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0011] In mobile radio systems, and especially in transmission systemswith CDMA (code division multiple access), power control is an importantfactor. In the transmission power, a compromise must be made between thetransmission quality and interfering with other subscribers. The higherthe transmission power, the better the transmission quality; and thelower the transmission power, the less are other subscribers interferedwith. It must also be remembered that a mobile station is generallybattery-operated. The operating time is thus dependent on the powerconsumption and hence also on the transmission power of the mobilestation.

[0012] Especially in CDMA transmission systems that areinterference-limited, as is the case with the UMTS (Universal MobileTelecommunications System), the system capacity, which can be expressedas the number of subscribers who are all active at the same time with aspecified connection quality, is dependent on regulating thetransmission power. The object of regulating the transmission power is,for every mobile radio connection, that is, both for a downlinktransmission direction from a base station to a mobile station and foran uplink transmission direction from the mobile station to the basestation, to adjust the transmission power individually in such a waythat a specified target value SIR_(z) in the signal/interference ratioSIR (signal to interference ratio) can be adhered to.

[0013] The UMTS will now be addressed as an example. In the UMTS, twodifferent duplex transmission methods across the air interface areprovided, as disclosed in the publication entitled “TS 25.201 V3.0.0:Physical Layer—General Description”, 3GPPP TSG-RAN-WG1, 1999. These twomethods are FDD (frequency division duplex) and TDD (time divisionduplex). In both, at least for the downlink transmission direction, aclosed control loop is provided for regulating the transmission power.

[0014]FIG. 1 shows as an example the block circuit diagram of a closedcontrol loop for regulating the transmission power P in a mobile radiosystem, such as UMTS. The control loop is identified in FIG. 1 byreference numeral 1. It includes a transmitting station 10 and areceiving station 20. Below, regulating the transmission power P foronly the downlink transmission direction will be addressed. In thisexample, for this purpose the transmitting station 10 is embodied as thebase station, and the receiving station 20 is embodied as the mobilestation of the UMTS. A downlink transmission channel from the basestation 10 to the mobile station 20 is identified in FIG. 1 by referencenumeral 31, and an uplink transmission channel from the mobile station20 to the base station 10 is identified in FIG. 1 by reference numeral32.

[0015] The base station 10 includes a first transmitting unit 14 and afirst receiving unit 11. The first receiving unit 11 communicates withthe first transmitting unit 14 via a first evaluation unit 12 and asecond evaluation unit 13. Other modules of the base station 10, whichare unnecessary to comprehension of the invention, are not shown in FIG.1 for the sake of simplicity. The mobile station 20 includes a secondreceiving unit 21 and a second transmitting unit 24. An SIR estimator 22is connected to the second receiving unit 21 and communicates with thesecond transmitting unit 24 via a third evaluation unit 23. Othermodules of the mobile station 20, which are unnecessary to comprehensionof the invention, are not shown in FIG. 1 for the sake of simplicity.

[0016] The invention will now be describe taking the TDD method as anexample. The base station 10, via the first transmitting unit 14, sendsa signal, at the transmission power P which is constant over a timeslot, to the mobile station 20 via the downlink transmission channel 31.This mobile station receives the signal by means of the second receivingunit 21. Next, the SIR estimator 22 ascertains the signal/interferenceratio SIR of the transmission. The third evaluation unit 23 performs acomparison of the estimated signal/interference ratio SIR with aspecified target value SIR_(z) for this ratio and as a function of thiscomparison generates TPC (transmit power control) instructions forchanging the transmission power P of the base station 10. By means ofthe TPC instructions, the only decision made is whether the transmissionpower P should be raised or lowered. Via the uplink transmission channel32, the TPC instructions are forwarded to the base station 10, alongwith other signals from the second transmitting unit 24.

[0017] In the base station 10, the signals and the TPC instructions arereceived by the first receiving unit 11 and sent on to the firstevaluation unit 12. The first evaluation unit 12 extracts the TPCinstructions from the signals received. The TPC instructions and thetransmission power P currently being used in the first transmitting unit14 are then sent to the second evaluation unit 13. In the secondevaluation unit 13, the amount of the change DeltaP in the transmissionpower P of the first transmitting unit 14 is then ascertained, in orderto adapt the transmission power P adaptively to the current propertiesof the downlink transmission channel 31.

[0018] In the current state of the specifications of the UMTS in thepublications entitled “TS 25.214 V3.0.0: Physical Layer Procedures(FDD)”, 3GPP TSG-RAN-WG 1, 1999 and “TS 25.215 V3.0.0: Physical LayerProcedures (TDD)”, 3GPP TSG-RAN-WG 1, 1999, the change DeltaP in thetransmission power P after a TPC instruction is received in thetransmitting station 10 is always made by only a predetermined amount,such as 1 dB. This means a nonlinear control, in which the actualdeviation in the signal/interference ratio SIR from the power ratioSIR_(z) is not taken into account. A decision is merely made whether thetransmission power will be raised or lowered by the specified value,such as 1 dB. As a result, it is not possible within only a few timeslots in the TDD method, by means of a corresponding increase in thetransmission power P of the transmitting station 10, to compensate forrapidly occurring, deep fading incursions of about 20 dB, for instance.

[0019] In FIG. 3, as an example, the amount of the reception fieldintensity E in the second receiving unit 21 is plotted in a solid lineover the time t for the situation without power control. This course,with deep incursions, is generally called “fast fading” and is typicalof mobile radio channels. The dashed line in FIG. 4 shows thetransmission power P theoretically required in the first transmittingunit 14 to obtain a constant signal level, at a constant interferencepower, in the second receiving unit 21, or in other words to compensatefor the effects of fading. The course of the transmission power P overtime t is the inverse of the course of the reception field intensity E.

[0020] In FIG. 3, a first time t1 is shown at which the transmissionpower P is low, because the amount of the reception field intensity E iscorrespondingly high. In the best case, then, a small change DeltaP inthe transmission power P, for instance by 1 dB, is needed in order toadapt the signal/interference ratio SIR, which has been measured by theSIR estimator 22, to the power ratio SIR_(z). According to theinvention, the amount of the change DeltaP in the transmission power Pis now to be made greater, if the transmission power P is increasing. Anincrease in the transmission power P is an indication that anattenuation incursion in the reception field intensity E has occurredand must be compensated for. As FIG. 3 shows, after the first time t1,the requisite transmission power P rises continuously up to a maximum ata fourth time t4. In FIG. 3, intermediate values in the transmissionpower P are found at a second time t2 and a third time t3, andt1<t2<t3<t4, and the requisite transmission power P to compensate forthe reception field intensity E becomes greater nonlinearly, with aninitially increasing rise. This means that the amount of the changeDeltaP must also rise from the first time t1 to the fourth time t4, ifthe course of the transmission power P shown in FIG. 3 is to be attainedand thus if the signal/interference ratio SIR ascertained in the SIRestimator 22 is to be adapted as fast as possible to thesignal/interference ratio SIR_(z).

[0021] Thus it can happen that a change DeltaP in the transmission powerP of 2 db, which is greater than the change DeltaP made at the firsttime t1, must already be made at time t3. At the fourth time t4, it canalso be provided that for the change DeltaP in the transmission power P,a value such as 4 db will be selected that is still greater than thechange DeltaP selected for the transmission power P at the precedingthird time t3.

[0022] To enable the fastest possible tracking of the transmission powerP to compensate for fading incursions as shown in FIG. 3, the changesDeltaP in the transmission power P must accordingly be selected as stillgreater, the higher the current transmission power P set at the firsttransmitting unit 14 is. This can be done for instance by means of anonlinear characteristic-curve as shown in FIG. 4, in which the amountof the change DeltaP in dB is plotted over the transmission power P ofthe first transmitting unit 14, for example, and the transmission powerP is also referred to an average over time Pmean in the transmissionpower P. The referral of the transmission power P to the average overtime Pmean is necessary, because the absolute value of the transmissionpower P also depends on the distance of the mobile station 20 from thebase station 10 and thus is not by itself conclusive as to incursions inthe course of the reception field intensity E. The average over timePmean in the transmission power P is formed from the values for thetransmission powers P of preceding time slots in the downlinktransmission channel 31 in the first transmitting unit 14.

[0023] In FIG. 4, the course of the amount of the change DeltaP in thetransmission power P is plotted over the power ratio P/Pmean, formedfrom the quotient of the transmission power P and the average over timePmean, in the form of a parabola branch whose apex is at the value pair(1/1). For values of the power ratio P/Pmean of between 0 and 1, a valueof 1 db is chosen in FIG. 4 for the amount of the change DeltaP in thetransmission power P. However, still other nonlinear relationshipsbetween the amount of the change DeltaP in the transmission power P andthe power ratio P/Pmean are conceivable. A nonlinear relationshipbetween the amount of the change DeltaP and the power ratio P/Pmeanmakes especially fast tracking of the signal/interference ratio SIR,estimated in the SIR estimator 22, to the specified target value SIR_(z)possible. Nevertheless, a linear relationship between the amount of thechange DeltaP and the power ratio P/Pmean, at which then the adaptationof the specified target value SIR_(z) in the case of abrupt fadingincursions cannot be tracked as fast as it can with a nonlinearrelationship, can also be selected.

[0024] The method for regulating the transmission power P will now beexplained in conjunction with FIG. 2, using a flowchart. Once atelecommunications connection between the base station 10 and the mobilestation 20 has been made, a starting value for the transmission power Pand an initial value for an increment size for the change DeltaP in thetransmission power P are first ascertained, at a program point 40. Thisincrement size can for instance amount to 1 dB, as shown in FIG. 4. Thestarting value for the transmission power P and the initial value forthe increment size of the change DeltaP in the transmission power P canbe selected by the first transmitting unit 14, for example. A jump isthen made to program point 41. At program point 41, the first receivingunit 11 checks whether the connection between the base station 10 andthe mobile station 20 still exists. One way this can be done is for thefirst receiving unit 11 to ask whether a disconnection request has beenreceived via the uplink transmission channel 32. If at program point 41the first receiving unit 11 ascertains that the connection still exists(YES decision), then a jump is made to a program point 42; if not (NOdecision), a departure from the program is made. At program point 42,the mean over time Pmean is formed from the values for the transmissionpower P from preceding time slots of the downlink transmission channel31. This averaging is done in the second evaluation unit 13. To thatend, the second evaluation unit 13 is also supplied with the currenttransmission power P from the first transmitting unit 14 of FIG. 1 andFIG. 2. At program point 41, the current transmission power P and theaverage over time Pmean, ascertained in program point 42, for the powerratio P/Pmean are also formed in the second evaluation unit 13.

[0025] As the characteristic curve in FIG. 4 shows, from the ascertainedpower ratio P/Pmean, the associated amount of the change DeltaP in thetransmission power P is determined. Then a jump is made to a programpoint 43. At program point 43, the second evaluation unit 13 checkswhether a TPC instruction was received via the uplink transmissionchannel 32. If so, a jump is made to a program point 44; if not, a jumpis made back to program point 41. At program point 44, the secondevaluation unit 13 knows, from the TPC instruction received, that thetransmission power P of the first transmitting unit 14 has to bechanged, and the received TPC instruction from the second evaluationunit 13 furthermore tells which sign this change has to have. The secondevaluation unit 13 at program point 44 thus causes the firsttransmitting unit 14 to change the transmission power P by the amount ofthe change DeltaP, ascertained at program point 42, in the transmissionpower P, and the sign for the change is specified by the TPC instructionreceived. A jump back to program point 41 is then made.

[0026] The method described can naturally also be used to control thetransmission power in the uplink transmission direction; in that case,reference numeral 10 would identify the mobile station, and referencenumeral 20 would identify the base station.

[0027] It can also be provided that the method of power regulationdescribed be used in both the uplink and the downlink directions oftransmission, and in this case not only the base station 10 but also themobile station 20 would have to have the first evaluation unit 12, thesecond evaluation unit 13, the third evaluation unit 23, and the SIRestimator 22, so that they will be able not only to perform a SIRestimation of the signals received and to generate a corresponding TPCinstruction, but also to achieve weighting of TPC instruction receivedand an adaptation of the transmission power P.

[0028] The method of the invention can also be used in an FDD system.

[0029] It is also noted that the use of the method of the invention in aUMTS is selected only as an example. The method of the invention canalso be used for instance in a GMS (Global System for MobileCommunications) mobile radio network.

1. A method for regulating the transmission power (P) of a transmittingstation (10) in a transmission system as a function of an estimate ofthe signal/interference ratio (SIR) in a receiving station (20), inwhich on the basis of an instruction (TPC) of the receiving station (20)the transmission power (P) in the transmitting station (10) is changed,characterized in that the amount of the change (DeltaP) in thetransmission power (P) is adjusted as a function of a power ratio(P/Pmean) between the current transmission power (P) and an average overtime (Pmean) in the transmission power (P), such that when the value ofthe power ratio (P/Pmean) is increasing, the amount of the change(DeltaP) in the transmission power (P) is also raised.
 2. The method ofclaim 1, characterized in that the relationship between the power ratio(P/Pmean) and the amount of the change (DeltaP) in the transmissionpower (P) is selected to be nonlinear.
 3. A transmitting station (10)for performing a method of one of claims 1 or 2, characterized in that areceiving station (11) is provided, which receives instructions (TPC)for changing (DeltaP) a transmission power (P) of the transmittingstation (10) from a receiving station (20), and that an evaluation unit(13) is provided, which changes the transmission power (P) of thetransmitting station (10) as a function of the instruction (TPC)received, and an amount of the change (DeltaP) in the transmission power(P) from a power ratio (P/Pmean) between the current transmission power(P) of the transmitting station (10) and an average over time (Pmean) inthe transmission power (P) of the transmitting station (10) is adjustedsuch that the amount of the change (DeltaP) in the transmission power(P) is raised when the value of the power ratio (P/Pmean) is increasing.4. The transmitting station (10) of claim 3, characterized in that therelationship between the power ratio (P/Pmean) and the amount of thechange (DeltaP) in the transmission power (P) is nonlinear.